Officers are warning the public to be vigilant about a group who are “trawling” Heath Drive and the Frognal and Fitzjohns area in search of elderly targets, who are offered a steam cleaning service.

Insp Howard Hornby, who is in charge of neighbourhood policing in north Camden, said: “This is a bogus service and it is likely, as we found on one occasion, an opportunity for them to basically ‘case’ the victim’s property.”

Insp Hornby said police came across the gang, said to be from the travelling community, three times last week.

On one occasion, police stopped three men and found two were wanted for other offences. An elderly resident told police that the men had insisted on taking a steam washer through his house.

When he went into the house to find them, they were coming out of his living room and claimed they had “got lost”.

Ins Hornby added: “Residents are asked to be aware of this group and call police if approached. This type of burglary is usually carried out on the elderly and infirm so is particularly cowardly.”